1. FIELD OF THE INVENTION
The invention relates to means for adjusting the timing of a valve, and is particularly but not exclusively applicable to internal combustion engines in which cyclically operated gas flow valves are used.
2. DESCRIPTION OF THE PRIOR ART
In conventional internal combustion engines, the gas flow valves, for example the inlet valves and exhaust valves of a four-stroke engine, are operated by mechanisms which open and close them at fixed timings, i.e. at the same number of degrees of crankshaft rotation before or after the top or bottom dead center positions of the piston, whatever the engine speed in revolutions per unit of time.
It has long been recognized that the overall performance of engines would be improved if the valves were open for a larger part of the cycle at high engine speeds than at low engine speeds. Several mechanisms have been proposed for this purpose and some have proved effective but they are too expensive, because of the complication, for use in mass-produced engines.
With the continuous demand for further improvements in engine performance, there is a need for an inexpensive mechanism for varying the open period of valves as the engine speed changes. More specifically, the chief requirements are to make the air valves close earlier at low engine speeds and the exhaust valves open later.